Retinal Prosthesis with Side Mounted Inductive Coil

ABSTRACT

The invention is a retinal prosthesis with an inductive coil mounted to the side of the eye by means of a strap around the eye. This allows for close coupling to an external coil and movement of the entire implanted portion with movement of the eye ball.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of U.S. patentapplication Ser. No. 11/498,506, filed Aug. 2, 2006, which is adivisional application of the U.S. patent application Ser. No.10/820,240, filed Apr. 6, 2004 the disclosure of which is incorporatedherein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01. The government has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to a visual prosthesis andmore specifically to an improved mechanical and electrical configurationfor retinal prosthesis for artificial vision.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930′s, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the information as a sequence of electricalpulses which are relayed to the nervous system via the prostheticdevice. In this way, it is possible to provide artificial sensationsincluding vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, and avoid undue compression of thevisual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Humayun, U.S. Pat. No.5,935,155 describes the use of retinal tacks to attach a retinal arrayto the retina. Alternatively, an electrode array may be attached bymagnets or glue. U.S. Pat. No. 5,109,844 to de Juan describes a flatelectrode array placed against the retina for visual stimulation.

Any device for stimulating percepts in the retina must receive a signaldescribing a visual image along with power to operate the device. Thedevice can not be powered by wires as any connection through the skinwill create the risk of infection. Battery power is not practical asbatteries are bulky and surgery is required to replace them. Such signaland power may be transmitted into the eye inductively as shown inHumayun U.S. Pat. No. 5,935,155. Humayun uses a primary (external) coilin front of the eye, possibly encased within the rim of a pair ofglasses, and a secondary (internal) coil within the lens capsule oraround the sclera just under the conjunctiva. Implanting within the lenscapsule is difficult surgery and only allows for a small diameter coil.Larger coils are more efficient, can receive more power with lessresulting temperature rise per unit of power received. Implanting aroundthe sclera under the conjunctiva and near the surgical limbus (that isat the front of the eye) allows for a larger coil but may causeirritation or damage to the conjunctiva if the coil is placed in frontnear the cornea.

U.S. patent application Ser. No. 09/761,270, Ok, discloses several coilconfigurations including a configuration where the coil is offset about45 degrees from the front of the eye. The offset configuration allowsthe primary and secondary coils to be placed closer together allowingfor better inductive coupling. The bridge of nose partially blocksplacement of a primary coil when placed directly in front of the eye.

A better configuration is needed allowing for close physical spacing ofrelatively large primary and secondary coils, without causing physicaldamages such as erosion of the conjunctiva.

SUMMARY OF THE INVENTION

The invention is a retinal prosthesis with an inductive coil mounted tothe side of the eye by means of a strap around the eye. This allows forclose coupling to an external coil and movement of the entire implantedportion with movement of the eye ball.

Applicants have discovered that a coil around the sclera at or near 90degrees rotation toward the lateral side of the eye has severaladvantages over previous designs. The secondary coil will not irritatethe conjunctiva as it is placed against the sclera under the lateralrectus muscle, well behind the region where the conjunctiva attaches tothe surgical limbus which is most susceptible to irritation. There isalso more room between the conjunctiva and sclera on the side of the eyecompared to the front of the eye. The primary coil can be placed on thetemples of a pair of glasses and/or hidden by the user's hair. Thespacing between primary and secondary coil can be as close, or closer,than that allowed for a coil pair located in the front of the eye or ata 45 degree angle because there are no eyelids or eyelashes to interferewith the coil.

The skull is relatively flat and thin at the temple outside the lateralside of the eye. This allows for close coupling of the primary andsecondary coils. The secondary coil can be mounted on the sclera underthe lateral rectus muscle allowing the coil to move with the eye,avoiding the need for a cable that flexes with eye movement.

A coil on the lateral side of the eye may be attached with a strapsimilar to a scleral buckle. A scleral buckle is a band of siliconeplaced around the eye and attached with a Watzke sleeve. A Watzke sleeveis a friction device that connects two silicone bands and holds themtogether with friction. Scleral buckles have been used to help hold thesclera against the retina when the retina has become detached. Scleralbuckles are well known and many surgeons are skilled in their use, butusing them to secure a device outside the eye is novel. Hence thesecondary coil can be attached to, or integrated with, the strap and thestrap placed around the sclera. In addition, suture tabs may be placedon the secondary coil to suture the coil to the sclera. The coil couldalso be affixed just by suturing to the sclera, without the use of abuckle.

In another alternative, the device may initially float and becomesecured by the growth of the natural foreign body reaction to thepresence of the device in the body.

Further, an implanted electronics package is required to process andsend the visual signal to the electrodes. It is advantageous to placethe electronics package outside the sclera to aid heat dissipation. Theelectronics package can be attached to the strap or directly to thecoil. This would not be possible with a front coil configuration asthere is not enough room under the conjunctiva to accommodate theelectronics package and coil near the limbus.

Blind people are conscious of their appearance. Hence, the reason forhiding the primary coil in a pair of glasses. A coil on the side of thehead can be hidden under the user's hair and/or incorporated in thedesign of glasses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 is a side view of the implanted portion of the preferred retinalprosthesis showing the fan tail in more detail.

FIG. 3 is an edge view of the implanted portion of the preferred retinalprosthesis showing the hook for aiding the implantation of the retinalprosthesis.

FIG. 4 is an external profile view of a user wearing the externalportion of the retinal prosthesis.

FIG. 5 shows an alternate embodiment using a passive repeater coil pair.

FIG. 6 show a second alternate embodiment using a coil in the templeregion of the scull.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. An electrode array 10 is mounted by aretinal tack or similar means to the epiretinal surface. The electrodearray 10 is electrically coupled by a cable 12 which pierces the scleraand is electrically coupled to an electronics package 14, external tothe sclera.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil may be madefrom a thin film polymer sandwich with wire traces deposited betweenlayers of thin film polymer. The electronics package 14 and secondaryinductive coil 16 are held together by a molded body 18. The molded body18 may also include suture tabs 20. The molded body narrows to form astrap 22 which surrounds the sclera and holds the molded body 18,secondary inductive coil 16, and electronics package 14 in place. Themolded body 18, suture tabs 20 and strap 22 are preferably an integratedunit made of silicone elastomer. Silicone elastomer can be formed in apre-curved shape to match the curvature of a typical sclera. However,silicone remains flexible enough to accommodate implantation and toadapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap can better support an oval shaped coil.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. It is an advantage of the present design, that the entireimplanted portion of the prosthesis is attached to and supported by thesclera. By placing the device under the rectus muscles with theelectronics package in an area of fatty issue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 2 shows a side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the fan tail 24. When implantingthe retinal prosthesis, it is necessary to pass the strap 22 under theeye muscles to surround the sclera. The secondary inductive coil 16 andmolded body 18 must also follow the strap under the lateral rectusmuscle on the side of the sclera. The implanted portion of the retinalprosthesis is very delicate. It is easy to tear the molded body 18 orbreak wires in the secondary inductive coil 16. In order to allow themolded body 18 to slide smoothly under the lateral rectus muscle, themolded body is shaped in the form of a fan tail 24 on the end oppositethe electronics package 14.

Reinforced attachment points 26 are provided to facilitate handling ofthe retinal prosthesis by surgical tools. Preferably, the reinforcedattachment points are harder silicone formed around holes through themolded body 18. Further, a hook 28 is molded into the strap 22 justbeyond the end of the fan tail 24. A surgical tool can be used againstthe hook 28 to push the strap 22 under the rectus muscles. The hook 28is more clearly depicted by the edge view of FIG. 3. The strap 22 isattached to itself by a sleeve 23. The sleeve 23 is a friction devicethat connects two silicone bands and holds them together with friction.The sleeve 23 is similar to a Watzke sleeve, used with a scleral buckle,and is well known in the art.

In the preferred embodiment, the electrode array 10 and cable 12 areformed layers of a thin polymer film with metal traces sandwichedbetween the thin polymer films. In such an embodiment, it isadvantageous that the film with openings for electrode array 10 be thesame film with an opening for connection to the electronics package 14.Therefore, the cable 12 exits the electronics package up away from thefantail 24, folds over itself and exits down toward the fantail 24,before turning at a right angle and piercing the sclera. This allows thesame side of the cable to face both the electronics package and theretina. The cable 12 may also include a fantail at the point it isattached to the electronics package 14 and at the point it is attachedto the electrode array 10 to reduce any stress on the connections thatmay be caused by implantation. It is important that the cable exit themolded body 18 toward the front of the eye. The cable must travel abovethe lateral rectus muscle and pierce the sclera at the pars plana, infront of the retina, so it does not damage the retina. Once inside theeye, the cable 12 can fold back over the retina to properly locate theelectrode array 10 on the epiretinal surface.

FIG. 4 depicts the profile of a user wearing the external portion of theretinal prosthesis. The entire device may be built into the temple of apair of glasses. A camera 30 collects a video image and transmits datato an external electronics package 32. A battery 34 powers the camera30, external electronics package 32, and provides power to a primaryinductive coil 36. The primary inductive coil 36 sends power and datathrough the skin and skull to the secondary inductive coil 16. Maximumefficiency is obtained when the primary inductive coil 36 and secondaryinductive coil 16 are the same size, shape and as close together aspossible.

Referring to FIG. 5, an alternate embodiment uses a passive repeatercoil pair. A passive secondary coil 42 is placed on the side of thescull in the temple region. Preferably, the passive secondary coil 42 ismounted just under the skin and attached to the temporalis muscle.Alternatively, the passive secondary coil 42 can be mounted wing ofspheroid 46 (bone) just under the temporalis muscle. Once attached,wires may be routed though the inferior orbital fissure 48 into the eyesocket 50, where a passive primary coil 44 is mounted to the scullinside the eye socket just over the lateral rectus muscle.

The passive secondary coil 42 and passive primary coil 44 form thepassive repeater coil pair. The passive repeater coil pair simply makesa more efficient path for power and data to travel from the primaryinductive coil 36 to the secondary inductive coil 16.

Referring to FIG. 6, a second alternate embodiment provides a remotesecondary to inductive coil 52, mounted the same as the passivesecondary coil 42. In this second alternative embodiment, wires from theremote secondary inductive coil 52 go directly to the electronicspackage 14. The electronics package 14 may be mounted with the remotesecondary inductive coil 52 or on the sclera like the preferredembodiment. In either case, this second alternative embodiment providesthe most efficient power use due to the close spacing of the primaryinductive coil 36 and remote secondary inductive coil 52. However, thisembodiment requires wires sufficiently flexible to accommodate eyemovement without work hardening to the point a breaking.

Accordingly, what has been shown is an improved retinal prosthesis.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is therefore tobe understood that within the scope of the claims, the invention may bepracticed otherwise than as specifically described herein.

1. A retinal prosthesis comprising: an electrode array suitable to bemounted in close proximity to a retina; an electronics package; anelectrical cable coupling said electrode array to said electronicspackage said electrical cable suitable to pierce the pars plana regionof the sclera; a secondary inductive coil, electrically coupled to saidelectronics package and suitable to be mounted to side of a sclera;wherein said cable and electrode array comprise metal traces sandwichedbetween thin polymer films.
 2. The retinal prosthesis according to claim1, further comprising a strap connected to said secondary inductive coiland surrounding the sclera.
 3. The retinal prosthesis according to claim1, further comprising a fan tail, having a decreasing radius ofcurvature, connected to said electronics package and to said cable tofacilitate passing said cable through the sclera.
 4. The retinalprosthesis according to claim 1, further comprising suture tabsconnected to said secondary inductive coil suitable for attaching saidsecondary inductive coil to a sclera.
 5. The retinal prosthesisaccording to claim 1, further comprising suture tabs connected to saidelectronics package suitable for attaching said electronics package to asclera.
 6. The retinal prosthesis according to claim 2, furthercomprising a fan tail connected to said secondary inductive coil and tosaid strap.
 7. The retinal prosthesis according to claim 2, furthercomprising a hook on said prosthesis suitable for engaging a surgicaltool.
 8. The retinal prosthesis according to claim 2, further comprisinga sleeve for attaching ends of said strap together.
 9. The retinalprosthesis according to claim 1, wherein said cable is folded to presentthe same side of said cable to both said electronics package and theretina.
 10. The retinal prosthesis according to claim 1, wherein saidelectrode array is suitable to placed in an epiretinal location.
 11. Theretinal prosthesis according to claim 1, wherein said secondaryinductive coil is a wound wire coil.
 12. The retinal prosthesisaccording to claim 1, wherein said secondary inductive coil issubstantially oval shaped.